Next Meeting

Date: 18 Sep 98

Time: "0845"-0945

Place: FEL Facility Break Room

Agenda for Next Meeting

                Item                             Person Responsible     Time
                ----                             ------------------  --------
Status of Open Action Items                             All             5 min
Commissioning Schedule                                  Bohn           10 min
Status of Gun                                           Biallas        10 min
Update on Hardware Changes/Additions                    Walker         10 min
Update on Software Changes/Additions                    Grippo         10 min
Recap of Recirculation/Lasing Procedure                 All            10 min
New Issues                                              All             5 min

This Week's Attendees

S. Benson, C. Bohn, J. Boyce, J. Delayen, D. Douglas, J. Fugitt, A. Grippo, K. Jordan, R. Lauze, L. Merminga, G. Neil, D. Oepts, J. Preble, M. Shinn, R. Walker, B. Yunn

Closed Action Items

None.

Items of Discussion

According to progress on refurbishing the gun, we should be able to pull beam off the gun on Friday, 18 Sep 98, although that could conceivably slip to the following Monday. The gun is being set up today for baking over the weekend.

C. Bohn formulated the commissioning plan for the next two weeks, and it can be found on the white board in the FEL Facility Break Room and (soon) on the www. Beam operations will begin in earnest on 21 Sep 98, with the following staffing:

Owl Shift: Piot, Hill (standby), 1 CEBAF operator;
Day Shift: Douglas, Benson (standby), 1 CEBAF operator;
Swing Shift: Walker, Shinn (standby), 1 CEBAF operator.

D. Douglas gave an excellent, well-organized presentation on his thoughts about the procedure for lasing cw with energy recovery. His thoughts were based on our accomplishments last month. The general idea, by necessity, is to concentrate on obtaining low-loss recirculated beam while containing it within the energy-recovery dump line. Most likely the difficulties we need to overcome are:

• poor dispersion profile in the back leg that, in turn, generates poor longitudinal match during energy recovery;
• possibly poor transverse match of the recirculated beam into the cryomodule (chromatic aberrations may lead to mismatch when the beam is far off momentum);
• insufficient configuration control (that arose due to the time pressure created by the upcoming FEL Conference, a situation that will not be present when we turn back on).

Using a simulation he wrote, Douglas showed how to compress a large energy spread after the wiggler into a small energy spread at the energy-recovery dump. The idea is to introduce quadratic nonlinearity, i.e., nonzero T_566, by reinjecting a long bunch length into the cryomodule so as to take advantage of the rf curvature for momentum compaction. To do so reduces to a phase-matching procedure that cannot rely on the cryomodule gang phase because the gang phase has to be set for achieving a minimal bunch length at the wiggler for strong lasing. Instead, it centers primarily on adjusting the path length that the beam follows through the recirculation loop.

As an aside, we have almost surely been running the injector such that a relatively long bunch length is injected into the cryomodule, after which the cryomodule considerably rotates the longitudinal phase space and shortens the bunch. This setup is compatible, if not even favorable, for energy recovery according to Douglas's simulation. Bohn had been conjecturing that this was the case since we have not yet seen a signal on Happek #1 at the entrance of the cryomodule. Of course, no definitive statement about injected bunch length can be made at this time.

Once the basic setup for strong lasing is established (starting in pulsed mode, of course), nothing prior to the wiggler can be touched. The available knobs for energy recovery are then:

• trim quadrupoles for M_56 adjustments,
• sextupoles for T_566 adjustments prior to reinjection into the cryomodule,
• trim dipole string for path length adjustments,
• reinjection (5F) quadrupoles for transversely matching the recirculated beam into the cryomodule,
• extraction dipole string (FELEXT) for centering the waste beam in the dump. All adjustments will need to be in small increments from the basic setup because the beam properties in the dump line are sensitive to all of these knobs.

Douglas will post his revised procedure on his FOTOMAT www page by Monday so it will be accessible for review, and he will have the final document by Friday, 18 Sep 98, so Bohn can then put hardcopies in the binders containing the FEL procedures for easy operator access. The aforementioned two-week commissioning plan is tailored to be consistent with this morning's discussion.

As a final note, B. Yunn agreed this week to try to extend his PARMELA deck to include the entire beamline past the wiggler for simulations of the beam dynamics with energy recovery. The code needs to be generalized to include sextupoles, and Yunn believes he can do so.

New Issues

None.

New Action Items

• Douglas: Post draft recirculation/lasing procedure on www (due 21 Sep 98), and finalize this procedure (due 25 Sep 98).
• Yunn: Generate PARMELA simulation of entire machine with energy recovery. (due 16 Oct 98)

Old Action Items

• Neil: Resolve safety and operations documentation issues associated with the conduct of user experiments.
  Status: Now have a general approach to laser safety in the user labs; presently drafting a form for users to fill out; will have LSS Review in early-mid Oct 98. (due 15 Oct 98, but lower priority than cw lasing with energy recovery)

  Bohn: Solidify strategy and plans for CSR experiments.

  Status: Discussions are continuing; for example, Bohn, R. Li, and B. Yunn met this week to plan content of CSR simulations around first arc. (due 30 Sep 98)

Procedures in Work

Tomographic Phase-Space Map (for CSR studies)             Piot, 31 Aug 98

Procedures Needed for Recirculation

RF Stability during Energy Recovery                       Merminga, 31 Aug 98

Unfinished Subsidiary Tasks for Phase Space Metaprocedure

Task                                                           Principal
----                                                           ---------
I.      Stabilize Drifts in Drive-Laser RF Phase               Walker/Fugitt

II.     Calibrate RF Gradients
        A.      Buncher                                        Yunn    
        B.      Cryounit Cavities (fix control screen)         Merminga/Krafft/Yunn
        C.      Cryomodule Cavities                            Merminga/Krafft/Yunn

III.    Reconcile Methods for Setting RF Phase                 Merminga/Krafft/Yunn
        A.      Buncher Cavities
                2.      Minimum bunch length/time of flight
                
        B.      Cryounit Cavities
                1.      Transient phasing
                2.      Cresting
                3.      Time of flight

IX.     Complete Diagnostics Procedures and  Users' Guide      Krafft/Piot
        A.      M_55 #1, #2
        B.      Happek #1, #2
        C.      BPMs
                1.      button calibration factors 
                2.      rotated MEDM spike charts
                3.      difference orbit data acquisition script
        D.      Multislit #1, #2
        E.      Quad/Viewer (at Wiggler, after Wiggler)
        F.      Multimonitor (at Wiggler)
        G.      SLM/CSR
        H.      Zero Phasing
        I.      Momentum Spread (Injector, Linac Pre-Wiggler, Linac Post-Wiggler)
        J.      Energy

XIV.    Laser Turn-On Procedure                                Benson